Retour au site du LAAS-CNRS

Abstract

This paper presents a methodology and tool based on 3D electro-thermal finite elements modeling intended to analyze the sequence of the events after emergence of defects in automotive power MOSFETs. Finite element modeling of power device and its nearby environment is detailed. The effects of delamination and bonding wire lift off on device transient electro-thermal behavior are investigated during a short circuit mode. Thus it helps to quantify the electro-thermal impact of the damages. Such modeling is useful for optimization of structure design to guarantee a longer lifespan.

Mots-Clés / Keywords

Power electronics; MOSFET; finite element modelling; Electro-thermal coupling; Device reliability;

Abstract

The presented work deals with high-density integrated capacitors for output filters in future micro DC-DC converters. In low power portable applications, integrated passive components are necessary to produce miniaturized systems. When talking about integrated capacitors, the current solutions on silicon (MOS or MIM) are not able to produce the capacitance values required for 1W DC-DC converter: more than 1uF/mm². To increase the capacitance density, the first approach is to work on the capacitor geometry: reduced dielectric thickness and maximised electrodes area. The second approach concerns the use of a high-k dielectric. In the presented work, we are combining these two approaches. 3D capacitors structures were realised with deep cavities network etched by DRIE in a high conductivity silicon substrate. The SiO2/Si3N4 standard dielectric [1] was replaced by ZrO2 (k =25- 40). The ZrO2 films (about 100 nm) were deposited by liquid injection MOCVD from Zr2(OiPr)6(thd)2. The following deposition parameters were studied: oxygen flow (0.05-0.1 l/min), substrate temperature (450°C-550°C), injection frequency (0.5-2 Hz), pressure (1-1000 Pa). The difficulty laid on the necessity to obtain at the same time uniform films (without cracks), good stoichiometry without carbon contaminants and good coverage in the deep silicon cavities. The stoichiometry and carbon contaminant were controlled by XPS, FTIR and SIMS. The ZrO2 thickness was measured by ellipsometry and by SEM on the cross-section of the cavities. The ZrO2 films deposited on silicon (100) were first characterized structurally by XRD. The films were constituted of a mixture of tetragonal and monoclinic phases. The deposition parameters were varied in order to promote the tetragonal phase (permittivity reported around 40 [2]). Low oxygen flow (0.05 l/min), low temperature (450°C), low injection frequency (0.5 Hz), low pressure (< 100 Pa) provided films with a predominant tetragonal phase. In parallel, the 3D coverage was observed in cavities with different depths (from 10 to 30 um) and widths (from 2 to 8 um). The thickness evolution was plotted versus the cavity aspect ratio (depth/width). It was shown that the ZrO2 thickness decreased to 20% - 30% of its surface value when the aspect ratio of the cavity was 2. For aspect ratio higher than 2, the thickness decreased only slightly. Electrical characterization of the ZrO2 films were done on two types of substrates: low resistivity Si (0.2 Ohm.cm) and Pt/Ti/SiO2/Si. The I(V), C(V) and C(frequency) characteristics for different deposition parameters allowed the evaluation of the leakage current (< 10e-6 A.cm-2), the permittivity (around 25), the breakdown voltage (300 kV/cm). These dielectric properties combined with 3D deposition will allow the realisation of very high-density capacitors.

Mots-Clés / Keywords

LPCVD-NiDoS films; Monte Carlo simulation; Boron implantation; GB interaction;

Abstract

We have studied the Ge-Si interdiffusion from structures in which not, vert, similar300 nm-thick pure Ge(:B) layers were grown on Si 200 mm substrates by CVD at 450 °C. As-grown samples were capped with SiO2 and then annealed in the 750-900 °C range for various times. Using the secondary ion mass spectrometry (SIMS) MCs2+ methodology, we measures precisely the Ge diffused profiles. Boltzmann-Matano analysis was used to extract the interdiffusion coefficients. Si-Ge interdiffusion is found to be strongly dependent on the Ge concentration. Also, an effect of dislocations near the Ge/Si original interface is suggested by our results. A physical model including the various observed effects is proposed, that gives a very good agreement with experiments. Finally, we show that the effect of the in situ B doping of the pure Ge layer is to reduce the interdiffusion.

Mots-Clés / Keywords

Interdiffusion; Germanium; Silicon; CVD; SIMS; MCs2+; Boltzmann-Matano; Defects; Modeling;

Mots-Clés / Keywords

Activation; Diffusivity; SIMS profile; Grain size; Boron;

Mots-Clés / Keywords

Polysilicon; Diffusion ; Model; SIMS profile;